1. Technical Field of Invention
The present invention relates generally to valves which may be used with mechanical seals.
More particularly, the present invention relates to a preferred, but not exclusive, application of the invention is to double mechanical seals in which a barrier or buffer fluid is used to lubricate and cool the components within the seal.
Reference will be made herein to mechanical seals and seal support systems, although it should be understood that valves of the invention have other applications.
2. Description of the Prior Art
A seal support system includes a vessel or tank containing a volume of fluid. The vessel is in piped connection to a mechanical seal which may be arranged to provide a seal within a pump or other item of rotating equipment. Normally, a return pipe extends from the mechanical seal back to the vessel. The resultant fluid loop is such that the fluid, contained within the vessel, may enter and exit the sealing device. Where a relatively large amount of heat is generated within the mechanical seal, a forced circulation system may be employed. In such a system barrier fluid is forced through the seal from the vessel by means of a pump and is then fed back to the vessel where the barrier fluid cools.
The AESSEAL PUMPPAC (registered trademark of AES Engineering Limited) is an arrangement which performs this task, having the ability to pressurise the barrier fluid being supplied to the mechanical seal. This ensures that, if there is any leakage across the seal face, it is always the barrier fluid which leaks in to the product, rather than the product (which may be hazardous to the environment) in to the atmosphere/vessel.
Typically the pressure of the barrier fluid is set 1 bar above that of the process fluid to ensure that, should leakage occur, it is in the manner indicated above.
It is known to provide a valve within the system in order to reduce the flow of barrier fluid to the seal when a pre-determined pressure difference is detected. However, if the product pressure varies but the back pressure applied to the barrier fluid is set at a fixed level, then excessive pressure within the mechanical seal may result in the seal having to work harder than is necessary, thereby causing the seal to deteriorate at a relatively fast rate.